The court said Nam Yimyaem's statements regarding Khunying Pojaman Shinawatra, wife of former prime minister Thaksin, were just legal opinions on corruption provisions.
"The comments in question were legal opinions on corruption provisions, hence the case has no cause for a judicial review on defamation," the ruling said.
As plaintiff, Pojaman sued both Nam in his capacity as chairman of the Asset Examination Committee and the Thai Post newspaper for publishing his remarks.
She alleged Nam had defamed her by drawing a comparison of her Ratchadaphisek land deal to a robbery.
The court ruled that Nam had merely explained graft provisions relevant to the land deal.
Nam's comments, when viewed as a whole, pointed out that a graft investigation involving Thaksin and Pojaman was based on abuse of power to acquire the plot, it said.
As the plot can be seized by the state if the Shinawatras are proven guilty, Nam gave his legal interpretation of the seizure of what in those circumstances would have been a stolen property as per Article 31 of the Criminal Procedural Code, it added.